1. Field of the Invention
The present invention relates to an elastic roller of off-right-circular cylinder with an elastic body being formed on a periphery of mandrel, which may be used, for example, as a fixing roller or a pressing roller of fixing unit, as a cleaning roller or a charge roller for photosensitive member, as a sheet feed roller of sheet feed unit in a copying machine or in a laser beam printer, and further as a platen roller in a printer or in a facsimile, to a unit using the elastic roller, to a method for producing the elastic roller, and to a molding apparatus of the elastic roller.
2. Related Background Art
In recent copying machines, printers, and facsimile machines which require high precision conveyance of record sheet by elastic rollers or in which an elastic roller must be pressed to contact with another member in a uniform nip width therebetween, the elastic roller is sometimes required to have a shape of off-right-circular cylinder which as used herein is one whose external form (i.e. diameter) varies in the longitudinal direction of elastic roller, such as of crown or of inverted crown to satisfy the requirements of conveyance of record sheet or others. For example, the elastic roller of crown may generally provide a high press contact force with a counter roller, and is often used in case of longer roller to prevent reduction of nip width in the central portion of roller bent as compared to that at the both ends. In contrast, an elastic roller of inverted crown is effective to prevent wrinkles on a record sheet, and is generally used for a relatively shorter roller in which a press contact force with a counter roller is small.
The following is conventional methods for producing such elastic rollers of off-right-circular cylinder.
(1) An elastic material is vulcanization-bonded on a periphery of mandrel of rod to form an elastic layer, and the elastic layer is shaped into a shape of off-right-circular cylinder by grinding to obtain an elastic roller of off-right-circular cylinder. PA1 (2) A through hole is perforated in a mold, for example, by a drill, and an internal surface of the hole is finished into the shape of off-right-circular cylinder by cutting and honing. A mandrel of rod is inserted into the finished hole through the mold and the both ends of mandrel are fixed on the mold through caps. Then an elastic material is filled into a space between the mold and the mandrel to form an elastic layer on a periphery of mandrel (see Japanese Patent Application Laid-open No. 1-174423). PA1 (3) A mandrel of rod is inserted into a hole of right circular cylinder having a constant inner diameter perforated in a mold, and the both ends of mandrel are fixed on the mold through caps. Then an elastic material is filled in a space between the mold and the mandrel, and thereafter vulcanized. Upon the vulcanization, a temperature of the mold is different along the axis of mandrel to differ thermal progress in vulcanization, so that an elastic layer of off-right-circular cylinder may be formed after mold release (Japanese Patent Application Laid-open No. 63-218982). PA1 an elastic roller of off-right-circular cylinder as used as the above-mentioned sheet feed roller; PA1 a stack member, on which a plurality of transfer members are stacked, for urging an uppermost transfer member stacked thereon, against the elastic roller; and PA1 separating means for separating the uppermost transfer member away from the other transfer members stacked on the stack member. PA1 an elastic roller of off-right-circular cylinder as used as the above-mentioned charge roller, the elastic roller being pressed to contact with an image carrying member in the copying machine or in the laser beam printer; and PA1 a power source for applying a voltage to the elastic roller. PA1 an elastic roller of off-right-circular cylinder as used as the above cleaning roller, the elastic roller being pressed to contact with an image carrying member in the copying machine or in the laser beam printer to scrape off residual toner on the image carrying member; and PA1 a toner storage section for storing the scraped-off residual toner. PA1 an elastic roller of off-right-circular cylinder as used as the above fixing roller. PA1 roller heating means provided inside the elastic roller; and PA1 an elastic roller of off-right-circular cylinder as used as the above pressing roller, which is urged against the former elastic roller. PA1 a step of producing a matrix shaped in the off-right-circular cylinder; PA1 a step of forming the mold by making a material for the mold adhered over a surface of a portion of off-right-circular cylinder of the matrix; and PA1 a step of dissolving to remove the matrix out of the formed mold. PA1 a step of producing a matrix shaped in the off-right-circular cylinder; PA1 a step of fixing respective annular reinforcements on both ends of periphery of off-right-circular cylinder of the matrix; PA1 a step of forming the mold by making a material for the mold adhered over a surface of a portion of off-right-circular cylinder of the matrix and of the reinforcements; and PA1 a step of dissolving to remove the matrix out of the formed mold, excluding the reinforcements. PA1 holding means covering to hold a mold produced by either of methods for producing an elastic roller of off-right-cylinder according to the present invention while being maintained at a constant temperature by heating means; PA1 injecting means for injecting an elastic material into the mold; and PA1 evacuating means for evacuating air in the mold.
The following problems are acknowledged on the above described conventional methods (1)-(3) for producing the elastic roller of off-right-circular cylinder.
In the method (1), it is difficult to grind the surface of elastic layer into the off-right-circular cylinder shape to obtain a surface finished in a desired surface roughness.
In the method (2), the grinding finish is unnecessary for the surface of elastic layer as is required in the method (1). It is, however, so difficult to finish the internal surface of longitudinally elongate hole with high precision into the off-right-circular cylinder shape by cutting and honing.
In the method (3), it is unnecessary to finish the hole of mold into the off-right-circular cylinder shape, as is required in the method (2). However, since the vulcanization has a great circumstance dependency, the elastic layer cannot be formed in a constant shape after mold release, and a molding duration is longer for a portion vulcanized at a low temperature.